WO2008069762 discloses a method for identifying a pathological region within a scan. The scan may be of any kind in which there is difference of intensity between normal and pathological regions. It particularly relates to a method for identifying brain scan slices that may include an acute ischemic stroke region, a method for distinguishing a brain hemisphere having the stroke region, and systems and software for performing the methods. The method analyses the intensity distribution of pixel values obtained as a result from the scan by a procedure including the following steps.
First the intensity distribution of each slice is determined, therewith obtaining a histogram specifying the frequency with which a certain pixel intensity occurs. Next percentile values are determined, i.e. indicating the pixel intensity below which a given percentage of all measured pixel intensities fall in the obtained histogram. A single parameter R is extracted from these percentile values by the following expression:
  R  =            P      50        ⁡          [                                    P                          b              +              20                                -                      P            b                                                P                          d              +              20                                -                      P            d                              ]      Therein Px indicates a percentile for a percentage x, and further b>50 and d<50. The value Pb+20−Pb is denoted the “bright band difference”, referring to the intensity difference between the top and bottom end of the “bright band” of the histogram and the value Pd+20−Pd is denoted the “dark band difference” referring to the intensity difference between the top and bottom end of the “dark band” of the histogram. Subsequently the difference obtained between the value of the parameter for the left hemisphere and the right hemisphere in a same slice are used as an indication of the presence of a pathological condition.
Whereas the known method may provide acceptable results for the type of pathological condition as considered in the above-cited WO2008069762, other pathological conditions may be less clearly visible, such as in early stages of dementia.
It is noted that WO 2011/142725 A1 discloses the analysis of brain functionality by comparing intensity distributions between brain hemispheres. Apart from intensity distributions, other characteristics include numerical parameters indicative of the characteristics of a body region such as percentiles and percentile ratios indicative for said intensity distributions.
It is further noted that Yoon et al. in “Quantitative analysis of groups-specific brain tissue probability map for schizophrenic patients”, discloses group-specific brain tissue probability maps derived from healthy control subjects and schizophrenic patients. This article is published in Neurolmage 26 (2005), pp 502-512.